If a running total is null then how to show 0.00?

Hi, I'm using Crystal Reports 8.5 and I have this issue:
I have a numeric running total field which is evaluated using a formula.
If no records satisfy that formula then the running total field becomes empty, but, instead of showing nothing (empty) I would like to show 0.00
How can I do this?

Thanks in advance

PS: I use visual basic 6.0 and reports are .rpt files outside of the .exe file.Ok, I solved it. I used a formula field which evaluates the running total, and I put the formula instead the running total on the report.|||How did you do that, Thanks.|||Create a formula having the code

If {RunningTotalField} is null then
0
else
{RunningTotalField}